1. Field of the Invention
The present invention relates generally to electrospray ionization mass spectrometry, and more specifically to a laser desorption electrospray ionization source that can improve the molecular ionization efficiency of a sample.
2. Description of the Related Art
Laser desorption ionization uses a pulse laser to irradiate sample molecules to vaporize and protonate them in preparation for carrying out mass spectrometry detection. One issue with known laser desorption approaches concerns laser intensity. When laser intensity is low, sample molecules do not easily produce ions. But when laser intensity is high, burning of droplets may result. At present, a conventional approach is to use a combination of laser thermal effects and electrospray ionization to form a laser desorption electrospray ionization source.
FIG. 1 shows an example of this prior scheme. As shown, an analyte placed on the target sample is irradiated to rapid evaporation with a certain frequency of laser pulses 70. Evaporation moves analyte molecules to a location between a Taylor cone tip of a hollow emission needle 10 and an ion transfer tube 13. The analyte molecules exchange charge with charged droplets formed by electrospraying to form ionized sample molecules, which may be drawn into the mass spectrometer 50 for analysis.